mcpc — a universal MCP CLI client

mcpc is a command-line client for the Model Context Protocol (MCP) that maps every MCP operation to an intuitive command for interactive shell use, scripting, and AI agents.

mcpc is your new Swiss Army knife for MCP. Reach for it to manually inspect and debug MCP servers, to script repeatable MCP workflows in plain shell, or to give AI coding agents the full power of modern MCP through the most universal interface there is: the UNIX shell.

Key features:

• 🔧 Full MCP support - Tools, prompts, resources, async tasks, skills, notifications, and logging over stdio and Streamable HTTP.
• 🔄 Persistent sessions - Keep multiple stateful connections to different servers alive in parallel.
• 🗺️ Progressive tool discovery - Find relevant MCP tools on the fly to save tokens and increase accuracy.
• 🔌 Code mode - JSON output composes with jq, xargs, and shell pipelines for MCP workflows as shell scripts.
• 🔒 Secure - Full OAuth 2.1 support with CIMD and DCR, uses OS keychain for credentials storage.
• 🤖 AI sandboxing - Proxy MCP server connections to protect credentials from AI-generated code.
• 🪶 Lightweight - Minimal dependencies, works on Mac/Win/Linux, doesn't use LLMs on its own.
• 💸 Agentic payments - Experimental support for the x402 protocol on Base.

Table of contents

• Motivation
• Install
• Quickstart
• Usage
• Sessions
• Authentication
• MCP proxy
• AI agents
• Agentic payments (x402)
• MCP support
• Configuration
• Security
• Errors
• Development
• Related work
• License

Motivation

Many AI agents misuse MCP. They treat tools as prompt-time function calls, repeatedly injecting tool definitions and results into the context. Tokens get wasted, context rots, the agent gets slower and less reliable, and popular conclusion that: "MCP sucks, CLIs are better".

mcpc challenges that narrative. It maps every MCP operation to an intuitive CLI command that agents pick up from --help alone. Any agent with shell access gets full MCP support without wiring up dozens of MCP functions. Just one Bash() tool, and mcpc handles the rest:

 ┌──────────┐   Bash()   ┌────────┐    MCP    ┌────────────┐
 │ AI agent │ ─────────► │  mcpc  │ ────────► │ MCP server │
 └──────────┘            └────────┘           └────────────┘
                                     Sessions, OAuth, Tools,
                                     Resources, Prompts,
                                     Tasks, x402, ...

CLI is the perfect local interface between agents and MCP, while MCP remains the standard remote interface for server discovery, authentication, payments, and access control. The two aren't exclusive – they're complementary.

As a bonus, the same mcpc configuration, OAuth profiles, and live sessions can be shared across many AI agents on the same machine. Authenticate once, reuse everywhere.

Install

Requires a JavaScript runtime — install the latest Node.js or Bun if you don't have one yet.

npm install -g @apify/mcpc

# Or with Bun
bun install -g @apify/mcpc

Linux: credentials use the OS keychain via the Secret Service API. GNOME/KDE desktops work out of the box. On headless/CI systems, mcpc falls back to a file-based store (~/.mcpc/credentials, mode 0600).

To force the keychain on headless systems, install libsecret + gnome-keyring (via apt-get, dnf, or pacman) and run:

dbus-run-session -- bash -c "echo -n 'password' | gnome-keyring-daemon --unlock && mcpc ..."

Quickstart

# List all active sessions and saved authentication profiles
mcpc

# Login to remote MCP server and save OAuth credentials for future use
mcpc login mcp.apify.com

# Create a persistent session and interact with it
mcpc connect mcp.apify.com @test
mcpc @test                                            # show server info
mcpc @test tools-list
mcpc @test tools-call search-actors keywords:="website crawler"

# Use JSON mode for scripting
mcpc --json @test tools-list

# Use a local MCP server package (stdio) referenced from config file
mcpc connect ./.vscode/mcp.json:filesystem @fs
mcpc @fs tools-list

Usage

Usage: mcpc [<@session>] [<command>] [options]

Universal command-line client for the Model Context Protocol (MCP).

Commands:
  connect [<server>] [@session]  Connect to an MCP server and start a new named @session
  close <@session>               Close a session
  restart <@session>             Restart a session (losing all state)
  login <server>                 Log in to a server and save an OAuth profile
  logout <server>                Delete an OAuth profile for a server
  clean [resources...]           Clean up mcpc data (sessions, profiles, logs, all)
  grep <pattern>                 Search tools and instructions across all active sessions
  x402 [subcommand] [args...]    Configure an x402 payment wallet (EXPERIMENTAL)
  help [command] [subcommand]    Show help for a command

Options:
  --json                         Output in JSON format for scripting
  --verbose                      Enable debug logging
  --profile <name>               OAuth profile for the server ("default" if not provided)
  --timeout <seconds>            Request timeout in seconds (default: 60)
  --max-chars <n>                Truncate output to n characters (ignored in --json mode)
  --insecure                     Skip TLS certificate verification (for self-signed certs)
  -v, --version                  Output the version number
  -h, --help                     Display help

MCP session commands (after connecting):
  <@session>                     Show MCP server info, capabilities, and tools overview
  <@session> grep <pattern>      Search tools and instructions
  <@session> tools-list          List all server tools
  <@session> tools-get <name>    Get tool details and schema
  <@session> tools-call <name> [arg:=val ... | <json> | <stdin]
  <@session> tasks-list
  <@session> tasks-get <taskId>
  <@session> tasks-result <taskId>
  <@session> tasks-cancel <taskId>
  <@session> prompts-list
  <@session> prompts-get <name> [arg:=val ... | <json> | <stdin]
  <@session> resources-list
  <@session> resources-read <uri> [-o <file> | --raw]
  <@session> resources-subscribe <uri> <file>
  <@session> resources-unsubscribe <uri>
  <@session> resources-templates-list
  <@session> skills-list
  <@session> skills-get <name> [--raw]
  <@session> logging-set-level <level>
  <@session> ping
  <@session> logs [-n N] [--follow] [--since 1h]

Run "mcpc" without arguments to show active sessions and OAuth profiles.
Run "mcpc --json" to get the same data as `{ sessions: [...], profiles: [...] }`.

Agent guide: mcpc help --skill

General actions

With no arguments, mcpc lists all active sessions and saved OAuth profiles:

# List all sessions and OAuth profiles (also in JSON mode)
mcpc
mcpc --json

# Show command help or version
mcpc --help
mcpc --version

# Clean stale sessions and old log files
mcpc clean

Server formats

The connect, login, and logout commands accept a <server> argument in these formats:

• Remote URL (e.g. mcp.apify.com or https://mcp.apify.com) — scheme defaults to https://
• Config file entry (e.g. ~/.vscode/mcp.json:filesystem) — file:entry-name syntax

connect additionally supports two bulk forms that connect many servers at once:

• Config file without an entry (e.g. ~/.vscode/mcp.json) — connect every server in the file
• No argument (mcpc connect) — auto-discover MCP config files in the current directory and your home dir (.mcp.json, mcp.json, .cursor/mcp.json, .vscode/mcp.json, ~/.claude.json, Claude Desktop, Windsurf, Kiro, …) and connect everything found (run mcpc connect --help for the full list).

mcpc connect                      # discover standard config files and connect all servers
mcpc connect ~/.vscode/mcp.json   # connect every server in one file

Bulk connects auto-generate session names (so they don't take an @session) and skip local stdio servers by default — pass --stdio to include them. Each discovered config file is listed with its servers and their status (● live, ● connecting); files that can't be used are shown as (0 servers) or (invalid) with the reason, rather than silently ignored. Without --json the command returns right away without waiting for every connection to finish (still-connecting sessions show ● connecting); --json waits and reports each server's details.

MCP commands

All MCP commands go through a named session created with connect:

# Connect to a remote server and create a session
mcpc connect mcp.apify.com @apify
mcpc @apify tools-list
mcpc @apify tools-call search-apify-docs query:="What are Actors?"

# Connect to a local server via config file entry
mcpc connect ~/.vscode/mcp.json:filesystem @fs
mcpc @fs tools-list
mcpc @fs tools-call list_directory path:=/

See MCP feature support for details about all supported MCP features and commands.

Command arguments

The tools-call and prompts-get commands accept arguments as positional parameters after the tool/prompt name:

# Key:=value pairs (auto-parsed: tries JSON, falls back to string)
mcpc @session tools-call <tool-name> greeting:="hello world" count:=10 enabled:=true
mcpc @session tools-call <tool-name> config:='{"key":"value"}' items:='[1,2,3]'

# Force string type with JSON quotes
mcpc @session tools-call <tool-name> id:='"123"' flag:='"true"'

# Inline JSON object (if first arg starts with { or [)
mcpc @session tools-call <tool-name> '{"greeting":"hello world","count":10}'

# Read from stdin (automatic when no positional args and input is piped)
echo '{"greeting":"hello","count":10}' | mcpc @session tools-call <tool-name>
cat args.json | mcpc @session tools-call <tool-name>

Auto-parsing rules for key:=value: valid JSON keeps its type (count:=10 → number, enabled:=true → boolean, cfg:='{"k":"v"}' → object); anything else is a string (greeting:=hello → "hello"). Force a string literal with JSON quotes: id:='"123"'. Inline JSON is detected when the first arg starts with { or [. Stdin is read when no positional args are given and input is piped.

Pitfalls: no spaces around := (use query:=hello world, not query := ...); quote the whole argument when it contains shell expansions ("query:=${VAR}"). For complex inputs, prefer piping JSON via stdin.

Grep (search across sessions)

mcpc grep searches tools, resources, and prompts across all active sessions or within a single session:

# Search tools and server instructions in all active sessions
mcpc grep "search"

# Search within a single session
mcpc @apify grep "actor"

# Search resources and prompts instead of the default tools and instructions
mcpc grep "config" --resources --prompts

# Regex search
mcpc grep "search|find" -E

# Case-sensitive search (default is case-insensitive)
mcpc grep "Search" --case-sensitive

# Limit results
mcpc grep "e" -m 5

# JSON output for scripting
mcpc grep "actor" --json

By default, grep searches only tools. Use --resources or --prompts to search those types (combine with --tools to include tools too). Sessions that are crashed or unavailable are shown with their status rather than silently skipped.

The grep command is useful for dynamic tool discovery, also called Tool search tool by Anthropic or Dynamic context discovery by Cursor. Rather than loading all tools into AI agent's context, the agent can use grep to discover the right tool for the job, and only load the relevant tools into the context when needed to reduce token usage and improve accuracy.

JSON mode

By default, mcpc prints output in Markdown-ish text format with colors, making it easy to read by both humans and AIs.

With --json option, mcpc always emits only a single JSON object (or array), to enable scripting. For all MCP commands, the returned objects are always consistent with the MCP specification. On success, the JSON object is printed to stdout, on error to stderr.

Note that --json is not available for login and mcpc --help commands.

Sessions

MCP is a stateful protocol: clients and servers negotiate protocol version and capabilities, and then communicate within a persistent session. To support these sessions, mcpc can start a lightweight bridge process that maintains the connection and state. This is more efficient than forcing every MCP command to reconnect and reinitialize, and enables long-term stateful sessions.

The sessions are given names prefixed with @ (e.g. @apify), which then serve as unique reference in commands.

# Create a persistent session
mcpc connect mcp.apify.com @apify

# List all sessions and OAuth profiles
mcpc

# Run MCP commands in the session
mcpc @apify tools-list

# Restart the session (kills and restarts the bridge process)
mcpc @apify restart    # or: mcpc restart @apify

# Close the session, terminates bridge process
mcpc @apify close      # or: mcpc close @apify

# ...now session name "@apify" is forgotten and available for future use

Session lifecycle

Session metadata is saved in ~/.mcpc/sessions.json, authentication tokens in the OS keychain. The bridge process keeps the session alive with periodic pings and auto-reconnects on network failures or its own crashes (10s cooldown on failed retries).

Session states:

mcpc never removes sessions automatically — failed ones stay flagged with a recovery hint in the error message. Use mcpc @apify restart to kill the bridge and open a fresh MCP-Session-Id, or mcpc @apify close to remove the session entirely. You can also remove dead sessions by running mcpc clean, and all sessions by running mcpc clean all (see Cleanup).

Authentication

mcpc supports all standard MCP authorization methods.

Anonymous access

For local servers (stdio) or remote servers (Streamable HTTP) which do not require credentials, mcpc can be used without authentication:

mcpc connect mcp.apify.com @test
mcpc @test tools-list

Bearer token authentication

For remote servers that require a Bearer token (but not OAuth), use the --header flag to pass the token. All headers are stored securely in the OS keychain for the session, but they are not saved as reusable OAuth profiles. This means --header needs to be provided whenever running a one-shot command or connecting new session.

# Create session with Bearer token (token saved to keychain for this session only)
mcpc connect https://mcp.apify.com @apify --header "Authorization: Bearer ${APIFY_TOKEN}"

# Use the session (Bearer token is loaded from keychain automatically)
mcpc @apify tools-list

OAuth profiles

For OAuth-enabled remote MCP servers, mcpc implements the full OAuth 2.1 flow with PKCE as mandated by the MCP authorization spec: WWW-Authenticate 401 challenges, Protected Resource Metadata and authorization server metadata discovery, all three client registration approaches, resource indicators (RFC 8707), and automatic refresh-token rotation.

The OAuth authentication always needs to be initiated by the user calling the login command, which opens a web browser with login screen. mcpc never opens the web browser on its own.

The OAuth credentials to specific servers are securely stored as authentication profiles - reusable credentials that allow you to:

• Authenticate once, use credentials across multiple commands or sessions
• Use different accounts (profiles) with the same server
• Manage credentials independently from sessions

Key concepts:

• Authentication profile: Named set of OAuth credentials for a specific server (stored in ~/.mcpc/profiles.json + OS keychain)
• Session: Active connection to a server that may reference an authentication profile (stored in ~/.mcpc/sessions.json)
• Default profile: When --profile is not specified, mcpc uses the authentication profile named default

Example:

# Login to server and save 'default' authentication profile for future use
mcpc login mcp.apify.com

# Use named authentication profile instead of 'default'
mcpc login mcp.apify.com --profile work

# Create two sessions using the two different credentials
mcpc connect mcp.apify.com @apify-personal
mcpc connect mcp.apify.com @apify-work --profile work

# Both sessions now work independently
mcpc @apify-personal tools-list  # Uses personal account
mcpc @apify-work tools-list      # Uses work account

# Re-authenticate existing profile (e.g., to refresh or change scopes)
mcpc login mcp.apify.com --profile work

# Delete "default" and "work" authentication profiles
mcpc logout mcp.apify.com
mcpc logout mcp.apify.com --profile work

Client registration approaches

When logging in, mcpc supports all three OAuth client registration approaches defined in the MCP authorization spec, picking the one the authorization server advertises in its OAuth metadata:

mcpc ships with a hosted Client ID Metadata Document so every installation presents the same client identity to CIMD-capable authorization servers. When the authorization server advertises client_id_metadata_document_supported: true, the CIMD URL is used as the client_id; otherwise mcpc falls back to Dynamic Client Registration.

# Default: mcpc's hosted CIMD is used automatically (no flags needed).
mcpc login mcp.apify.com

# Pre-registered OAuth client (public or confidential) — skips CIMD.
mcpc login mcp.example.com --client-id <id> [--client-secret <secret>]

# Pre-registered client whose redirect URI was registered with localhost
# instead of 127.0.0.1 (e.g. http://localhost:3118/callback).
mcpc login mcp.example.com --client-id <id> --callback-host localhost --callback-port 3118

# Custom CIMD: override the default with your own hosted document.
mcpc login mcp.example.com --client-metadata-url https://example.com/my-client.json

# Disable CIMD: force Dynamic Client Registration even if the server supports CIMD.
mcpc login mcp.example.com --no-client-metadata-url

See the MCP authorization spec for details on each approach and the format of Client ID Metadata Documents.

Authentication precedence

When connecting, mcpc picks one auth source based on the flags you pass — explicit flags always win over stored profiles, and credentials are never silently downgraded. If a profile is missing, expired, or invalid, mcpc fails with an error that includes the right mcpc login command to recover.

Config file headers (from --config) apply to servers loaded from that file.

# Default: 'default' profile if it exists, else anonymous
mcpc connect mcp.apify.com @apify-personal

# Specific profile (fails if missing)
mcpc connect mcp.apify.com @apify-work --profile work

# Explicit bearer token (no profile)
mcpc connect mcp.apify.com @apify --header "Authorization: Bearer ${APIFY_TOKEN}"

# Skip default profile, connect anonymously
mcpc connect mcp.apify.com @apify-anon --no-profile

# x402 micropayments instead of OAuth
mcpc connect mcp.apify.com @apify --x402

MCP proxy

For stronger isolation, mcpc can expose an MCP session under a new local proxy MCP server using the --proxy option. The proxy forwards all MCP requests to the upstream server but never exposes the original authentication tokens to the client. This is useful when you want to give someone or something MCP access without revealing your credentials. See also AI sandboxes.

# Human authenticates to a remote server
mcpc login mcp.apify.com

# Create authenticated session with proxy server on localhost:8080
mcpc connect mcp.apify.com @open-relay --proxy 8080

# Now any MCP client can connect to proxy like to a regular MCP server
# The client has NO access to the original OAuth tokens or HTTP headers
# Note: localhost/127.0.0.1 URLs default to http:// (no scheme needed)
mcpc connect localhost:8080 @sandboxed
mcpc @sandboxed tools-call search-actors keywords:="web scraper"

# Optionally protect proxy with bearer token for better security (stored in OS keychain)
mcpc connect mcp.apify.com @secure-relay --proxy 8081 --proxy-bearer-token secret123
# To use the proxy, caller needs to pass the bearer token in HTTP header
mcpc connect localhost:8081 @sandboxed2 --header "Authorization: Bearer secret123"

Proxy options for connect command:

Security model:

• Localhost by default: --proxy 8080 binds to 127.0.0.1 only, preventing network access
• Tokens hidden: Original OAuth tokens and/or HTTP headers are never exposed to proxy clients
• Optional auth: Use --proxy-bearer-token to add another layer of security
• Explicit opt-in: Proxy only starts when --proxy flag is provided

Binding to network interfaces:

# Localhost only (default, most secure)
mcpc connect mcp.apify.com @relay --proxy 8080

# Bind to all interfaces (allows network access - use with caution!)
mcpc connect mcp.apify.com @relay --proxy 0.0.0.0:8080

# Bind to specific interface
mcpc connect mcp.apify.com @relay --proxy 192.168.1.100:8080

When listing sessions, proxy info is displayed prominently:

mcpc
# @relay → https://mcp.apify.com (HTTP, OAuth: default) [proxy: 127.0.0.1:8080]

AI agents

mcpc is designed for CLI-enabled AI agents like Claude Code or Codex CLI, supporting both interactive tool calling and code mode.

Tool calling mode - Agents call mcpc commands to dynamically explore and interact with MCP servers, using the default text output. This is similar to how MCP connectors in ChatGPT or Claude work, but CLI gives you more flexibility and longer operation timeouts.

# Discover available tools
mcpc @server tools-list

# Get tool schema
mcpc @server tools-get search

# Call a tool
mcpc @server tools-call search query:="hello world"

Code mode - Once agents understand the server's capabilities, they can write shell scripts that compose multiple mcpc commands with --json output — see Scripting below. This can be more accurate and use fewer tokens than tool calling for complex workflows. Pair with schema validation to catch breaking changes early.

Scripting

Use --json for machine-readable output (stdout on success, stderr on error). JSON output of all MCP commands follows the MCP specification strictly.

# Chain tools across sessions
mcpc --json @apify tools-call search-actors keywords:="scraper" \
  | jq '.content[0].text | fromjson | .items[0].id' \
  | xargs -I {} mcpc @apify tools-call get-actor actorId:="{}"

# Batch operations
for tool in $(mcpc --json @server tools-list | jq -r '.[].name'); do
  mcpc --json @server tools-get "$tool" > "schemas/$tool.json"
done

For a complete example script, see docs/examples/company-lookup.sh.

Schema validation

The tools-get and tools-call commands support --schema to validate a tool's schema against an expected snapshot. This helps detect breaking changes early in scripts and CI:

# Save expected schema
mcpc --json @apify tools-get search-actors > expected.json

# Validate without calling (read-only check)
mcpc @apify tools-get search-actors --schema expected.json

# Validate before calling (fails if schema changed incompatibly)
mcpc @apify tools-call search-actors --schema expected.json keywords:="test"

Available schema validation modes (--schema-mode):

• compatible (default)
  • Input schema: new optional fields OK, required fields must have the same type.
  • Output schema: new fields OK, removed required fields cause error.
• strict - Both input and output schemas must match exactly, including all fields, types, and descriptions
• ignore - Skip validation completely (YOLO)

AI sandboxes

To ensure AI coding agents don't perform destructive actions or leak credentials, it's always a good idea to run them in a code sandbox with limited access to your resources.

The proxy MCP server feature provides a security boundary for AI agents:

1. Human creates authentication profile: mcpc login mcp.apify.com --profile ai-access
2. Human creates session: mcpc connect mcp.apify.com @ai-sandbox --profile ai-access --proxy 8080
3. AI runs inside a sandbox: If sandbox has access limited to localhost:8080, it can only interact with the MCP server through the @ai-sandbox session, without access to the original OAuth credentials, HTTP headers, or mcpc configuration.

This ensures AI agents operate only with pre-authorized credentials, preventing unauthorized access to MCP servers. The human controls which servers the AI can access and with what permissions (OAuth scopes).

IMPORTANT: Beware that MCP proxy will not make an insecure MCP server secure. Local stdio servers will still have access to your local system, and HTTP servers to provided auth credentials, and both can easily perform destructive actions or leak credentials on their own, or let MCP clients do such actions. Always use only trusted local and remote MCP servers and limit their access to the necessary minimum.

Agent skills

mcpc ships a built-in agent skill that always matches the installed version:

mcpc help --skill

No setup is needed: mcpc help mentions mcpc help --skill, so an agent can discover and load the guide on its own when it needs it.

If you'd rather have the skill installed persistently (e.g. for Claude Code or any agent that loads SKILL.md files), mcpc help --skill prints a valid SKILL.md — just redirect it into your skills directory:

mkdir -p ~/.claude/skills/mcpc
mcpc help --skill > ~/.claude/skills/mcpc/SKILL.md

That copy is a snapshot; re-run it after upgrading mcpc to refresh it.

Separately, mcpc also acts as a client for skills served by MCP servers (experimental, SEP-2640) — see Skills for the skills-list / skills-get commands.

Agentic payments (x402)

⚠️ Experimental. This feature is under active development and may change.

mcpc has experimental support for the x402 payment protocol, which enables AI agents to autonomously pay for MCP tool calls using cryptocurrency. When an MCP server charges for a tool call (HTTP 402), mcpc automatically signs a USDC payment on the Base blockchain and retries the request — no human intervention needed.

This is entirely opt-in: existing functionality is unaffected unless you explicitly pass the --x402 flag.

How it works

Two schemes are supported, both signed by your local wallet:

• exact — EIP-3009 TransferWithAuthorization. Settles on-chain at call-time.
• upto — Permit2 PermitWitnessTransferFrom. You sign a max cap; the facilitator settles accumulated usage later. First use auto-grants a one-time USDC.approve(PERMIT2, MAX_UINT256) (needs a tiny native ETH float for gas).

Flow: server returns HTTP 402 with a PAYMENT-REQUIRED header → mcpc picks the best scheme per your preference, signs, and retries with PAYMENT-SIGNATURE → server verifies and fulfills. Tools that advertise pricing in _meta.x402 are signed proactively, skipping the 402 round-trip.

Wallet setup

mcpc stores a single wallet in ~/.mcpc/wallets.json (file permissions 0600). You need to create or import a wallet before using x402 payments.

# Create a new wallet (generates a random private key)
mcpc x402 init

# Or import an existing wallet from a private key
mcpc x402 import <private-key>

# Show wallet address and creation date
mcpc x402 info

# Remove the wallet
mcpc x402 remove

After creating a wallet, fund it with USDC on Base (mainnet or Sepolia testnet) to enable payments.

Manual payment signing

You can manually sign a payment from a server's PAYMENT-REQUIRED header using x402 sign. This is useful for pre-signing payments or integrating with tools outside of mcpc.

# Sign a payment using the base64-encoded PAYMENT-REQUIRED header
mcpc x402 sign <base64-payment-required>

# Override the amount (in USD, e.g. 2.50 = $2.50)
mcpc x402 sign <base64-payment-required> --amount 2.50

# Override the expiry (in seconds from now)
mcpc x402 sign <base64-payment-required> --expiry 7200

# Combine overrides and use JSON output
mcpc x402 sign <base64-payment-required> --amount 1.00 --expiry 3600 --json

Options:

The command outputs the signed PAYMENT-SIGNATURE header value and an MCP config snippet that can be used directly with other MCP clients.

Using x402 with MCP servers

Pass the --x402 flag when connecting to a session. It accepts an optional scheme preference (auto, upto, or exact); bare --x402 defaults to auto.

# Create a session with x402 payment support (auto picks the best advertised scheme)
mcpc connect mcp.apify.com @apify --x402

# Pin a specific scheme — position doesn't matter, before or after positional args
mcpc connect --x402 upto mcp.apify.com @apify
mcpc connect mcp.apify.com @apify --x402 exact

# The session now automatically handles 402 responses using your preference
mcpc @apify tools-call expensive-tool query:="hello"

# Restart re-uses the saved scheme from sessions.json — no need to repeat the flag
mcpc @apify restart

When --x402 is active, a fetch middleware wraps all HTTP requests to the MCP server. If any request returns HTTP 402, the middleware transparently signs and retries. Your scheme preference is persisted in sessions.json and reused on every reconnect or restart.

Supported networks

MCP support

mcpc aims to be the most complete MCP client on the command line. It's built on the official MCP SDK for TypeScript and supports all the major client-facing features of the MCP specification, from tools, resources, and prompts to the newest additions like async tasks and skills. Each is exposed as a first-class command with consistent human-readable and --json output.

MCP feature support

Where mcpc stands on each part of the MCP specification:

Beyond the interactive browser login, the Authorization row above also covers the OAuth client-credentials grant (the io.modelcontextprotocol/oauth-client-credentials extension) for non-interactive, machine-to-machine use such as CI/CD and daemons — no browser: mcpc login <server> --grant client-credentials --client-id <id> --client-secret <secret> (or a private-key JWT assertion via --client-key, RFC 7523). Access tokens are fetched and refreshed automatically; pin a non-discoverable token endpoint with --token-endpoint <url>.

Server instructions

MCP servers can provide instructions describing their capabilities and usage. These are displayed when you connect to a server or run the help command:

# Show server info, capabilities, and instructions (both commands behave the same)
mcpc @apify
mcpc @apify help

# JSON mode
mcpc @apify --json

In JSON mode, the resulting object adheres to InitializeResult object schema, and includes the _mcpc field with relevant server/session metadata.

{
  "_mcpc": {
    "sessionName": "@apify",
    "profileName": "default",
    "server": {
      "url": "https://mcp.apify.com"
    },
    "notifications": {
      "tools": { "listChangedAt": "2026-01-01T00:42:58.049Z" }
    }
  },
  "protocolVersion": "2025-06-18",
  "capabilities": {
    "logging": {},
    "prompts": {},
    "resources": {},
    "tools": { "listChanged": true }
  },
  "serverInfo": {
    "name": "apify-mcp-server",
    "version": "1.0.0"
  },
  "instructions": "Apify is the largest marketplace of tools for web scraping..."
}

Tools

Tools are the heart of MCP, and mcpc gives you the whole toolbox to discover, inspect, validate, and call them:

# List tools (compact view): names, one-line descriptions, and safety/task hints
mcpc @apify tools-list

# List tools with full input/output schemas and descriptions
mcpc @apify tools-list --full

# Inspect a single tool's schema, annotations, and a ready-to-run example
mcpc @apify tools-get search-actors

# Call a tool with arguments
mcpc @apify tools-call search-actors keywords:="web scraper"

# Pass complex JSON arguments
mcpc @apify tools-call create-task '{"name": "my-task", "options": {"memory": 1024}}'

# Load arguments from stdin
cat data.json | mcpc @apify tools-call bulk-import

The compact tools-list is built for progressive tool discovery: instead of loading every tool's full schema into an agent's context up front, list just names and summaries, use mcpc grep to find the right tool for the task, and pull its full schema with tools-get only when you need it. Fewer tokens, less context rot, better accuracy. And listings never go stale: the session bridge handles tools/list_changed notifications and refreshes its cache automatically, so you always see the server's current tools.

mcpc surfaces everything modern MCP tools can express:

• Safety annotations: read-only, destructive, idempotent, and open-world hints are shown right next to each tool, so a human or an agent can tell a harmless query from a dangerous mutation before calling it.
• Structured output: structuredContent is pretty-printed as JSON and output schemas are shown with --full, so scripts can rely on machine-readable results, not just text.
• Rich result content: text, images, audio, and resource links or embedded resources in tool results are all rendered (binary is summarized, never dumped to your terminal).
• Async tasks: long-running tools can run in the background as async tasks; each tool's task support is flagged as [task:optional], [task:required], or [task:forbidden].
• Schema validation: pin a tool's schema with --schema to catch breaking changes in CI and scripts before they bite (see Schema validation).

Prompts

List and retrieve server-defined prompt templates:

# List available prompts
mcpc @apify prompts-list

# Get a prompt with arguments
mcpc @apify prompts-get analyze-website url:=https://example.com

Resources

Access server-provided data sources by URI:

# List available resources
mcpc @apify resources-list

# Read a resource (pretty view; binary content is summarized, never dumped)
mcpc @apify resources-read "file:///config.json"

# Print just the content for piping
mcpc @apify resources-read "file:///config.json" --raw | jq .

# Save a resource to a local file (binary-safe, decodes base64 blobs)
mcpc @apify resources-read "file:///logo.png" -o logo.png

# List resource templates
mcpc @apify resources-templates-list

Subscriptions keep a local file in sync with a server resource. On subscribe, mcpc downloads the resource to the file; afterwards the session bridge rewrites the file whenever the server sends a notifications/resources/updated notification for the URI (the bridge re-reads the resource, as the notification carries no content). Requires the server capability resources.subscribe; subscriptions are re-established automatically when the session reconnects or restarts, and are listed in mcpc @session output.

# Keep ./config.json in sync with the server resource
mcpc @apify resources-subscribe "file:///config.json" ./config.json

# Stop syncing — the local file is kept as-is
mcpc @apify resources-unsubscribe "file:///config.json"

Skills

🧪 Experimental. Implements the draft MCP skills extension (SEP-2640). The spec is in active iteration; the index shape, recognized entry types, and capability key may change.

Agent Skills are reusable markdown workflow instructions (SKILL.md with YAML frontmatter) that AI agents load on demand. mcpc lets you discover and pull skills served by any MCP server that exposes them under the skill:// URI convention — no SDK changes required, since skills are just resources:

# List skills exposed by the server (tries skill://index.json, falls back to scanning skill://*/SKILL.md)
mcpc @apify skills-list

# Read a skill's SKILL.md by bare name, nested path, or full URI
mcpc @apify skills-get git-workflow
mcpc @apify skills-get acme/billing/refunds
mcpc @apify skills-get skill://git-workflow/SKILL.md

# Print just the markdown (no header/fences) — pipe straight to an LLM or a file
mcpc @apify skills-get git-workflow --raw > /tmp/skill.md

# JSON for scripts: [{ name, description, type, url }]
mcpc --json @apify skills-list | jq '.[].name'

Recognized index entry types (per SEP-2640): skill-md (concrete skill), mcp-resource-template (parameterized namespace), and archive (.tar.gz/.zip bundle — fetch the URL via resources-read). Entries with an unrecognized type are silently skipped.

Skills appear under capabilities in mcpc @session output when a server advertises the extension under either capabilities.extensions["io.modelcontextprotocol/skills"] (per spec) or capabilities.experimental["io.modelcontextprotocol/skills"] (the SDK-preserved escape hatch some SDKs still use). Skill content is treated as untrusted input — mcpc only reads and prints it; it never executes hooks, scripts, or other frontmatter-declared behavior.

List change notifications

When connected via a session, mcpc automatically handles list_changed notifications for tools, resources, and prompts. The bridge process tracks when each notification type was last received. The timestamps are available in JSON output of mcpc @session --json under the _mcpc.notifications field - see Server instructions.

Server logs

mcpc supports server logging settings (logging/setLevel) and log messages (notifications/message). Log messages are printed to bridge log or stderr, subject to verbosity level.

You can instruct MCP servers to adjust their logging level using the logging-set-level command:

# Set server log level to debug for detailed output
mcpc @apify logging-set-level debug

# Reduce server logging to only errors
mcpc @apify logging-set-level error

Note that this sets the logging level on the server side. The actual log output depends on the server's implementation.

Pagination

MCP servers may return paginated results for list operations (tools-list, resources-list, prompts-list, resources-templates-list). mcpc handles this automatically and always fetches all available pages using the nextCursor token - you always get the complete list without manual iteration. Keep it simple.

Ping

Sessions automatically send periodic pings to keep the connection alive and detect failures early. Send a ping to check if a server connection is alive:

# Ping a session and measure round-trip time
mcpc @apify ping
mcpc @apify ping --json

Async tasks

MCP servers can execute tools as async tasks that run in the background and report progress. mcpc supports the full task lifecycle:

# Call a tool as a task (waits for completion, shows progress spinner)
mcpc @apify tools-call long-running-job input:="data" --task

# Start a task and return immediately with the task ID
mcpc @apify tools-call long-running-job input:="data" --detach

# List active tasks
mcpc @apify tasks-list

# Check task status
mcpc @apify tasks-get <taskId>

# Get the task result (blocks until the task reaches a terminal state)
mcpc @apify tasks-result <taskId>

# Cancel a running task
mcpc @apify tasks-cancel <taskId>

With --task, the CLI shows a progress spinner with elapsed time, server status messages, and progress notifications. Press ESC during execution to detach and get the task ID for later retrieval. With --detach, the task starts and returns the task ID immediately. Use tasks-result <taskId> to fetch the final CallToolResult payload once the task completes.

tools-list and tools-get show task support annotations per tool: [task:optional], [task:required], or [task:forbidden].

Configuration

You can configure mcpc using a config file, environment variables, or command-line flags.

Precedence (highest to lowest):

1. Command-line flags (including --config option)
2. Environment variables
3. Built-in defaults

MCP server config file

mcpc supports the "standard" MCP server JSON config file, compatible with Claude Desktop, VS Code, and other MCP clients. Use the file:entry syntax to reference a server from a config file:

# Open a session to a server specified in the Visual Studio Code config
mcpc connect .vscode/mcp.json:apify @my-apify
mcpc @my-apify tools-list

mcpc also finds these files for you: run mcpc connect with no arguments to auto-discover config files in standard locations and connect every server, or pass a file without an entry to connect all of its servers. See Server formats.

Example MCP config JSON file:

{
  "mcpServers": {
    "apify": {
      "url": "https://mcp.apify.com",
      "headers": {
        "Authorization": "Bearer ${APIFY_TOKEN}"
      }
    },
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/tmp"],
      "env": {
        "DEBUG": "mcp:*"
      }
    },
    "local-package": {
      "command": "node",
      "args": ["/path/to/server.js"]
    }
  }
}

Server configuration properties:

For Streamable HTTP servers:

• url (required) - MCP server endpoint URL
• headers (optional) - HTTP headers to include with requests
• timeout (optional) - Request timeout in seconds

For stdio servers:

• command (required) - Command to execute (e.g., node, npx, python)
• args (optional) - Array of command arguments
• env (optional) - Environment variables for the process

Note: Stdio servers inherit only a minimal env whitelist from the shell (PATH, HOME, SHELL, …). Other vars — NODE_EXTRA_CA_CERTS, HTTPS_PROXY, SSL_CERT_FILE, etc. — must be forwarded explicitly via the env block using ${VAR_NAME}. Anything the server writes to stderr is captured to ~/.mcpc/logs/bridge-<session>.log with a [server stderr] prefix, and the tail is appended to the error message if mcpc connect fails, so you can see why a stdio server failed to start.

Environment variable substitution:

Config files support environment variable substitution using ${VAR_NAME} syntax:

{
  "mcpServers": {
    "secure-server": {
      "url": "https://mcp.apify.com",
      "headers": {
        "Authorization": "Bearer ${APIFY_TOKEN}",
        "X-User-ID": "${USER_ID}"
      }
    }
  }
}

Saved state

mcpc saves its state to ~/.mcpc/ directory (unless overridden by MCPC_HOME_DIR), in the following files:

• ~/.mcpc/sessions.json - Active sessions with references to authentication profiles (file-locked for concurrent access)
• ~/.mcpc/profiles.json - Authentication profiles (OAuth metadata, scopes, expiry)
• ~/.mcpc/wallets.json - x402 wallet data (file permissions 0600)
• ~/.mcpc/bridges/ - Unix domain socket files for each bridge process
• ~/.mcpc/logs/bridge-*.log - Log files for each bridge process
• OS keychain - Sensitive credentials (OAuth tokens, bearer tokens, client secrets)

Environment variables

• MCPC_HOME_DIR - Directory for session and authentication profiles data (default is ~/.mcpc)
• MCPC_VERBOSE - Enable verbose logging (set to 1, true, or yes, case-insensitive)
• MCPC_JSON - Enable JSON output (set to 1, true, or yes, case-insensitive)
• HTTPS_PROXY / https_proxy / HTTP_PROXY / http_proxy - Proxy URL for outbound connections (e.g. http://proxy.example.com:8080); HTTPS_PROXY takes precedence
• NO_PROXY / no_proxy - Comma-separated list of hostnames/IPs to bypass the proxy (e.g. localhost,127.0.0.1)

Cleanup

You can clean up the mcpc state and data using the clean command:

# Safe non-destructive cleanup: remove expired sessions, delete old orphaned logs
mcpc clean

# Clean specific resources
mcpc clean sessions    # Kill bridges, delete all sessions
mcpc clean profiles    # Delete all authentication profiles
mcpc clean logs        # Delete all log files

# Nuclear option: remove everything
mcpc clean all         # Delete all sessions, profiles, logs, and sockets

Security

mcpc follows MCP security best practices. MCP enables arbitrary tool execution and data access - treat servers like you treat shells:

• Use least-privilege tokens/headers
• Only use trusted servers!
• Audit tools before running them

Credential protection

Network security

• HTTPS enforced for remote servers (auto-upgraded from HTTP)
• OAuth callback binds to 127.0.0.1 only
• Credentials never logged, even in verbose mode

AI security

See AI sandboxes for details.

Errors

mcpc provides clear error messages for common issues:

• Connection failures: Displays transport-level errors with retry suggestions
• Session timeouts: Automatically attempts to reconnect or prompts for session recreation
• Invalid commands: Shows available commands and correct syntax
• Tool execution errors: Returns server error messages with context
• Bridge crashes: Detects and cleans up orphaned processes, offers restart

Exit codes

• 0 - Success
• 1 - Client error (invalid arguments, command not found, etc.)
• 2 - Server error (tool execution failed, resource not found, etc.)
• 3 - Network error (connection failed, timeout, etc.)
• 4 - Authentication error (invalid credentials, forbidden, etc.)

Verbose mode

To see what's happening, enable detailed logging with --verbose.

mcpc --verbose @apify tools-list

This causes mcpc to print detailed debug messages to stderr.

Logs

View the bridge log for a session with mcpc @<session> logs (run with --help for --follow, -n, and --since options). The underlying file lives at ~/.mcpc/logs/bridge-@<session>.log and is rotated automatically (10MB per file, max 5 files). The main mcpc process doesn't save log files, but supports verbose mode.

Troubleshooting

"Cannot connect to bridge"

• Bridge may have crashed. Try: mcpc @<session-name> tools-list to restart the bridge
• Check bridge is running: ps aux | grep -e 'mcpc-bridge' -e '[m]cpc/dist/bridge'
• Check socket exists: ls ~/.mcpc/bridges/

"Session not found"

• List existing sessions: mcpc
• Create new session if expired: mcpc @<session-name> close and mcpc connect <server> @<session-name>

"Authentication failed"

• List saved OAuth profiles: mcpc
• Re-authenticate: mcpc login <server> [--profile <name>]
• For bearer tokens: provide --header "Authorization: Bearer ${TOKEN}" again

Development

The initial version of mcpc was developed and launched by Jan Curn of Apify with the help of Claude Code, during late nights over Christmas 2025 in North Beach, San Francisco.

See CONTRIBUTING for development setup, architecture overview, and contribution guidelines.

Related work

MCP CLI clients